Many chemical reactions can be accelerated under high pressure, high temperature conditions. Generally apparatus for generating high pressures and temperatures require high pressure pumps and vessels. Such apparatus is relatively complex, expensive and hazardous due to the abrasive nature of most aqueous waste.
Apparatus with subsurface, vertical downgoing and upgoing flow passages connected together at the bottom to form a long U-tube use a hydrostatic column to generate high pressures for accelerating chemical reactions. Generally these reactors consist of a pair of concentric, cylindrical, vertical tubes that extend deep underground. The reactants pumped into the top of one tube flow down that tube to the bottom, up the other tube and out the top of the other tube. In these reactors the downgoing and upgoing tube are generally in heat exchange relation to each other so that heat from the reaction in the up flowing fluid heats the down flowing fluid.
U.S. Pat. No. 4,272,383 to the present applicant, incorporated herein by reference, discloses such a reactor and method particularly suitable forreacting waste streams such as sewage sludge, animal waste and other oxidizable fluids. In the disclosed apparatus, air was injected at about ground level in the form of “Taylor bubbles” and a heat exchanger in the reaction zone in the lower portion of the reactor controlled the temperature. At a pressure above 135 psi and a temperature greater than 350° F., these waste streams are hydrolyzed, breaking down the organic components into lighter molecular weight molecules. With sufficient temperature, pressure, time and oxygen, the organic molecules will essentially convert to carbon dioxide, water and heat.
In prior known vertical subsurface reactors the heat transferred from the up flowing fluid to the down flowing fluid was insufficient for the reaction to be self-sustaining or thermally autogenous. In these reactors, heat was continually added through the heat exchanger to sustain the reaction or the injected air was replaced with liquid oxygen to increase heat recovery, significantly increasing costs and safety concerns.